Perimeter Security: Trip Wire Alarms (Part IV)

In previous discussions, we’ve talked about encouraging an intruder to a specific area where he can be observed, and how we’re going to slow him down once he gets to the gaps we’ve created. At this point, according to the laid-out plan in parts I-III, you’re going to hit the intruder with a thorny hedge, and-or fence, and-or stumble wire. Unless he’s undisciplined, chances are you may not hear an “ouch” if you’re at the house, barn, or sleeping in your bed; and maybe your dog won’t either. So how does any of this do more than maybeslow down the intruder? You’re going to alarm that stumble wire. You can also just set up trip wires in the gaps, or arrange them in gaps in the stumble wire.

The trip wires will go six inches and twelve inches off the ground, using fishing wire, artificial sinew, or a single strand from inside the Paracord. In addition, you may want some up at knee or thigh height, so that smaller animals don’t set them off. I’ve seen YouTube videos where people set them up at thigh height. I don’t really endorse that, because even my less-lean, less-than-coordinated, ruined-knees body can be made to quietly slide underneath a wire at thigh and hip level. I can also, even with the glasses, see that wire more readily. What I do endorse is the “other” rule of threes (you know, have 3 ways to accomplish everything). Instead of laying one trip wire, I may lay them in sets of three that are parallel to each other and 3, 6 or 9 inches apart, to maximize a foot snagging them.

Once you’ve decided on lines and placement, there are a couple of things you can use as alarms.

Alarm types

I agree wholeheartedly with perimeter security that focused on low-tech options. Even if I have a generator, and solar, and a Gasifier, I want to conserve fuel. I shake my head at that cameras and security systems I see on TV regularly. I can barely make my email work, but that’s only part of the problem.

Door alarms

One option is the battery-operated types that go on doors. It’s going to need a charger for batteries. They’re not pricey, neither the alarms nor the chargers nor NiMH batteries. When the cord is stepped on, it pulls a bar away from the base and an alarm peals out. The base piece needs a post or the ground nearby. The tripwire is attached to the bar. Some of them completely detach, some of them pivot. Being wrapped in Saran wrap can help keep the base piece in better shape as it’s exposed to damp and wet weather, and the thin plastic doesn’t disrupt the magnet that holds the bar on.

The downside is door alarms are less robust in outdoor conditions and requires batteries, so you have to have a backup for each spot with these alarms, backup batteries for each primary and backup alarm, and a way to charge the batteries.

Insert Video: https://www.youtube.com/watch?v=QMB4m41IXfA

Chem light-rat trap

Another option is using rat traps and chem lights. For them, the wire gets attached to the rat trap trigger and the chem light gets tied or taped where the rat usually gets popped. When the rat trap is triggered, it snaps the chem light, activating it. There’s no audio alert, which is good and bad. Good, the bad guy doesn’t always know he’s been made, especially if there are small limbs he’s already been stepping on, which could explain away the tension from the wire and the sound of the rat trap snapping. Because there’s no audio alarm, though, somebody has to be able to see the trap and chem light. This means they’re really only effective at night. It’s a really simple alarm, requiring just two uprights (trees or posts or stakes in the ground), tape or cordage to hold the base to one, and cordage to stretch across to the other.

To build that type, you’re going to run the trip wire from between two trees or posts (this is the activation zone; I actually like double or triple lines at two heights to improve my chances of it being triggered). There’s going to be a nail or an eye hook to change the angle of the wire and run it up the tree or post to a height that it can be observed by someone on guard. You’re going to have to check periodically that no squirrels have triggered the trap, that no tree limbs or birds’ nests are blocking it, and that nothing has run away with the trap or chem light. You want to not needlessly break a raccoon’s leg or kill a songbird. If the needless death doesn’t bother you, consider that they both eat garden pests.

This system is inexpensive enough, rat traps are pretty sturdy and cheap enough to replace and will run almost forever as long as the rust stays cleaned off, but the weak link is the chem light. Also inexpensive in bulk, but eventually they stop working. There’s a shelf life not just after they’re snapped (they have glow lives of 2-24 hours depending on what you buy) but also to get them to activate at all. It’s hard to know exactly when they were manufactured since they’re not required to be marked, so you could have one to five years of usefulness out of them from the day they’re purchased. It’s worth the risk to me for many applications, not just alarms.

A variation to this method, and one that costs more, is a Cyalume Surface Trip Flare which also uses a chem light. Please watch the following video for a demonstration.

Solar-powered floodlights

You also have the option to install solar-powered, motion-activated spotlights, just like the ones outside garages all over mainstream America. They need to go somewhere that they receive enough light for at least twelve hours of darkness, more if you live in an area with significant stretches of winter with only eight hours of daylight. There is the possibility that they can be taken out with a quiet slingshot or well-thrown brick. The bulbs need backups and having a couple of spares wouldn’t be a bad idea. Still, there’s not a lot of moving parts to most of them and once they’re up, if they’re looked in on and the solar collector is cleaned here and there, they’re pretty hand’s free. They will immediately tell the intruder they’re being watched, but they’ll also tell the neighborhood and intruder that something is being watched. On their own with a fence, they might not be all that effective, so I would still employ the stumble wire and hedges or brambles. Consider them a warning device, an alert, and position them to watch your perimeter; don’t be lulled and think a light offers safety.

Homemade noisemakers

An alternative to alarms that need a lot of maintenance or materials is pretty darn simple. In among your tangle wire you’re going to leave some long strands, wrapped once around posts and only tied off in one location, on one side. The other side you’re going to run up something like a tree, on the house side of the yard. It’s going to get twitched over a short nail or peg with no rim. You want it to slip off relatively easily. You’re going to attach a jar or can of marbles, ball bearings or some other round, heavy object. That jar is going to be situated above two baking sheets. One is going to be a foot or more off the ground and positioned so just the corner gets hit by the jar. You can add some glass bottles, empty tin cans, or other marbles or metal if you want, so long as the suspended jar (attached to the trip/stumble wire) is heavy enough to tip that first pan. You want the jars and bottles upside down so they don’t collect water when it rains. Below that, on the ground, you’re going to have another pan positioned as a landing pad for the suspended jar and the raised pan. This is all to maximize noise.

When the stumble wire gets run into or cut, you want the jar to get jerked off the peg or to fall. The noise is the alarm. You can also try stringing multiple empty tin cans together above a pot or pan, improving the noise by putting a little mud in the bottom of them. Empty glass bottles will make noise, too, if they fall on metal. The broken glass may be a bonus or a negative to you. You could arrange it so that a brick or rock is falling on a pyramid of glass bottles and metal cans. You could have a cow bell attached to all the stumble wire and trip wires and have a few tied in with some metal rods cut down from T-posts, heavy metal spoons, glass and metal pot lids, or even a few frying pans. The goal is to have something loud enough that if it went off inside your house you could hear it in your sleep and loud enough to wake your dog or carry to whoever is standing sentry at night. It’s not foolproof, not perfect, but it is pretty sustainable and it can be done pretty inexpensively.

About the Author: R.S.N. is a former Marine Corps combat correspondent with overseas experience. After the service, her interests turned to sustainability in growing and in maximizing the produce from small spaces.